Electrical contact element



July 23, i

R. H. SAVAGE ELECTRICAL CONTACT ELEMENT Filed June 21, 1941 His AttorneyPatented July 23, 1946 ELECTRICAL CONTACT ELEMENT Robert H. Savage,Scotia, N. X, .asvsignortp .Gen-

eral Electric Company, a corporation of New York Application June 21,1941, Serial No. 399,193

32 Claims. 1

My invention relates to electrical contact element and particularly toimproved contact brushes and methods of making the same.

An object of my invention is to provide an improved electrical contactelement.

Another object of my invention is to provide an improved electricalcontact element formed of a porous block of electrically conductivematerial provided with a lubricant for the contact surface thereof.

A further object of my invention is to provide an improved method ofmaking an electrical con tact element.

Further objects and advantage of my invention will become apparent andmy invention Will be better understood from the following descriptionreferring to the accompanying drawing, and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

The single figure in the drawing illustrates a contact brush for adynamo-electric machine embodying my invention and made in accordancewith my improved method of construction.

It has been found that under normal atmospheric conditions with averagehumidity, atmospheric water vapor provides the best known lubricant forthe contact surfaces of carbon and metal-graphite brushes. It has alsobeen found that electrical contact elements made of porous blocks offinely divided electrically conductive material, such as carbon or metaland graphite brushes, tend to wear away very rapidly in dry atmospheres.,In the past different lubricants have been suggested for minimizing thefriction of the contact surface of the brushes and thereby improving thelife of the contact element, but so far as is now known, these variouslubricants do not prevent brushes from wearing away rapidly in dryatmospheres. Furthermore, most of the lubricants which have beensuggested disadvantageously change the electrical characteristics of thebrush or combine with the contact element material to form substanceswhich impede the free movement of thecontact element on its .guidemember or brush holder, thereby decreasing the .efiiciency of operationof the combination. I have found that impregnating a porous block ofelectrically conductive material with a humectant which has thecharacteristic of wetting the brush material even in the absence ofwater in the impregnating material, such as apolyhydric alcohol oralcohol-ether or mixtures of these in at least a portion of the block,to provide a lubricant for the contact surface thereof greatly increasesthe life of the porous block, especially in dry atmospheres.Furthermore, it have found that under certain conditions and for certaintypes of materials, the contact element is improved by applying to thesides thereof a coat of relatively thin material Which will not form apaste with the impregnant of the contact element when the brush vibratesand moves on its guiding surface.

In the drawing, I have shown an electrical contact element formed as anelectric current collectorbrush including a porous block I0 of bondedfinely divided electrically conductive carbonaceous material, such ascarbon, graphite, metalgraphite, or other similar material including asubstantial amount of carbon such as is conventionally used in themanufacture of contact elements, such as commutator and slip-ringbrushes. A terminal clip II is secured to the porous block ID by a rivetI2 and an electrically conductive pigtail member i3 is secured to theterminal clip I I and to a connecting terminal element M for conductingcurrent between a brush holder connector and the contact element blockIn. In order to provide a lubricant to the contact surface I5 ofthe'porous block II], a portion of the block below the terminal clip II, or the entire porous block i8, is impregnated with a pol'yhydricalcohol or alcohol-ether solution. Among the polyhyd-ric alcohol whichhave been found to provide an efficient lubricant for the contactsurface of the brush I0, I have found the ethylene glycols-tobe-particularly efiicient. Mixtures of different polyh-ydric alcoholsalso have good lubricating properties. These impregnants are highly "hgroscopic and water soluble and have .a relatively Wide liquid statetemperature range. Generally, they also have the desirable properties ofa relatively high flash point and a relatively low vapor pressure atnormal contact element operating temperatures. For certain types ofelectrically conductive materials, such ascarbon, .electro-graphitic, ornatural graphite brushes, I have found a solution of from 10% to 30 ofnonaethylene glycol in water to be a'very efficient impregnant,especially if the metal content of the brush is 50% .or less. Forcontact elements wherein the porous material comprises a'very largeamount of metal, or more, I have found that an impregnant comprising 40%to 60% nonaethylene glycol and 3 l 20% to 30% polyolefin glycol in wateris a very efiicient lubricant.

In forming my improved contact elements, I have found it desirable todegas the porous block by subjecting it to a relatively low pressure andthen impregnating the degassed block with the lubricant, after whichexcess impregnant is removed from theblock, and, in certain cases, arelatively thin coating of'material, which does not react with theimpregnant, is applied to the sides of the dried block. In degassing theporous block, the contact element is immersed in a solution of theimpregnant, such as a 20% to 40% solution of nonaethylene glycol inwater or benzene, and the block is subjected to a relatively lowpressure in this solution for from one to two hours, such that the wateror benzene comesto a boil, removing the gas from the porous block. Afterthis treatment, a part or the whole of the'porous block is impregnatedat substantially atmospheric pressure with the solution of polyhydricalcohol in water or benzene for from one to two hours. Excess impregnantthen is removed from the outside of the block in any suitable manner, asby wiping or draining. The block then may be dried at a 4 5. A moldedelectrical contact element including a graphitic block, and having aportion of said block impregnated with an ethylene glycol solution as alubricant fOr the contact surface of said element.

6. An electrical contact element including a,

' current collector brush formed of a porous carbonaceous block, andhaving at least a portion of said block impregnated with glycerol as alubricant for the contact surface of the element.

8. An electrical contact element including a I current collector brushformed of a porous cartemperature between .70" and 120 C. to removewater from the brush and to provide the desired concentration ofimpregnant. As stated above,

with certain porous materials, it is desirable to provide a very thincoating of non-paste forming material over the sides of the block. Ihave found that a thin coating of metal of between 5 and 10 milsthickness applied to the sides of the block by spraying molten metalunder pressure, as by the Schoop process provides an efficientlowfriction surface which will not form a paste with the impregnant,even after long periods of use and vibration over a supporting orguiding sur-. face. This metal preferably is of relatively highelectrical conductivity, such as copper, and may or may not be porous. Ametal coating of this type provides a relatively hard guiding surfacefor the brush on its brush holder and effectively prevents sticking ofthe brush in the holder.

=While I have illustrated and described particular embodiments of myinvention, modifications thereof will occur to those skilled in the art(I desire it to be understood, therefore, that my invention is not to belimited to the particular arrangements disclosed, and I intend intheappended claims to cover all modificationswhich do not depart fromthe spirit and scope of my invention. I

' What I claim as new and desire to secure by Letters Patent of theUnited States is:

4 1. An electrical contact element including a current collector brushformed of a porous block of finely divided electrically conductivecarbonaceous material, and a solution comprising ethylene glycolsolution in at least a portion of said porous block.

a 2. A molded electricalcontactelement including a block of finelydivided carbon, and an ethylene glycol solution in at least a portion ofsaid block.

3. An electrical contact element including a current collector brushformed of a porous member of finely divided bonded carbonaceousmaterial, and an ethylene glycol solution in at least a portion of saidporous member. 4. An electrical contact element including a porousgraphitic block, and an ethylene glycol impregnated into at least aportion of said porous block..

' hygroscopic lubricant for. the contact surface or bonaceous block, andhaving at least a portion of said block impregnated with a higherboiling point glycol as a lubricant fOr the contact surface of theelement. 7

9. An electrical contact element including a current collector brushformed of a porous carbonaceous block, and having at least a portion ofsaid block impregnated with polyolefin glycol as a lubricant for thecontact surface of the element;

10. An electrical contact element including a current collector brushformed of a porous block of electrically conductive carbonaceousmaterial; and having at least a portion of said block impregnated with ahygroscopic humectant material characterized by the property of wettingsaid brush material in the absence of water in said impregnatingmaterial.

11. An electrical contact element including a current collector brushformed of a porous carbonaceous block, and having at least a portion ofsaid block impregnated with a highly hygroscopic material characterizedby the property of wetting said carbonaceous material of said brush inthe absence of water in said impregnating material and having arelatively low vapor pressure at normal contact element operatingtemperatures.

12. A brush element including a porous carbonaceous block of finelydivided electrically conductive material, a humectant in at least aportion of said porous block, and means including a relatively thincoating on the sides of said block for preventing the formation of apaste by said humectant and said finely divided material.

13. A molded electrical contact element including a graphitic block, andhaving a portion of said block impregnated with nonaethylene glycol as alubricant for the contact surface of said element.

14. A brush element including a porous block of electrically conductivecarbonaceous material, and having at least a portion of said blockimpregnated with an alcohol-ether solution as a lubricant for thecontact urface of the element.

15. A brush element including a porous carbonaceous block, and having atleast a portion of said block impregnated with a highly hygroscopicv ofwater in said impregnating material and hava relatively high flashpoint.

16'. An electrical contact element including a porous block of finelydivided electrically conductive carbonaceous material, at least aportion of said block being impregnated with a highly said element, andmeans including a relatively thin coating on the sides of said block forpreventing the formation of a paste by said impregnant and said finelydivided material.

17. An electrical contact element including a porous block of finelydivided electrically conductive material, at least a portion of saidblock having a liquid lubricant therein for the contact surface of saidelement, and means including a coating on the sides of said block havingthe characteristics of a coating applied by spraying under pressure onthe sides of said block for preventing the formation of a paste by saidimpregnant and said finely divided material.

18. An electrical contact element including a porous block of finelydivided electrically conductive carbonaceous material, at least aportion of said block being impregnated with a polyhydric alcoholsolution providing a lubricant for the contact surface of said element,and means including a relatively thin coating on the sides of said blockfor preventing the formation of a paste by said impregnant and saidfinely divided material.

19. An electrical contact element including a porous block of finelydivided electrically conductive material, at least a portion of saidblock having a lubricant therein for the contact surface of saidelement, and a metallic coating on the sides of said block having thecharacteristics of a coating applied by spraying under pressure on thesides of said block.

20. An electrical contact element including a porous block of finelydivided electrically conductive carbonaceous material, at least aportion of said block being impregnated with a polyhydric alcoholsolution providing a lubricant for the contact surface of said element,and a metallic coating on the sides of said block.

21. A brush element including a porous block of electrically conductivematerial, and an impregnant in at least a portion of said blockcomprising a solution of nonaethylene glycol and polyolefin glycol inwater.

22. A brush element including a porous block of electrically conductivematerial, and an impregnant in at least a portion of said blockcomprising a solution of substantially 50% nonaethylene glycol andsubstantially polyolefin glycol in substantially 25% water.

23. A brush element including a porous block of electrically conductivematerial, and an impregnant in at least a portion of said blockcomprising a solution of substantially nonaethylene glycol in water.

24. The method of making an electrical contact element including forminga porous block, degassing the porous carbonaceous block, andimpregnating at least a part of the degassed porous block with apolyhydric alcohol solution.

25. The method of making an electrical contact element including forminga porous block, impregnating at least a part of the porous block with apolyhydric alcohol solution, and applying to the sides of theimpregnated block by spraying under pressure a relatively thin coatingof material non-paste forming with the impregnant.

26. The method of making an electrical contact element including forminga porous block, degassing the porous block, impregnating at least a partof the degassed porous block with a polyhydric alcohol solution, andapplying to the sides of the impregnated block a relatively thin coatingof material non-paste forming with the impregnant.

27. The method of making an electrical contact element including forminga porous block, impregnating at least a part of the porous block with apolyhydric alcohol solution, and applying by spraying under pressure arelatively thin coating of metal to the sides of the impregnated block.

28. The method of making an electrical contact element including forminga porous block of electrically conductive material, degassing the porousblock by subjecting it to a relatively low pressure, impregnating atleast a part of the degassed porous block with nonaethylene glycol,removing excess impregnant from the block, and applying to the sides ofthe dried block a relatively thin coating of material non-paste formingwith the impregnant.

29. The method of making an electrical contact element including forminga porous block of electrically conductive material, degassing the porousblock by subjecting it to a relatively low pressure, impregnating atleast a part of the degassed porous block with a polyhydric alcoholsolution, removing excess impregnant from the block, and applying arelatively thin coating of metal to the sides of the dried block.

30. The method of making an electrical contact element including forminga porous block of electrically conductive material, degassing the porousblock by subjecting it to a relatively low pressure, impregnating atleast a part of the degassed porous block with a solution ofnonaethylene glycol and polyolefin glycol, removing excess impregnantfrom the block, and applying to the sides of the dried block arelatively thin coating of from 5 to 10 mils thickness of materialnon-paste forming with the impregnant.

31. The method of making an electrical contact element including forminga porous block of electrically conductive material, degassing the porousblock by subjecting it to a relatively low pressure for from one to twohours, impregnating at least a part of the degassed porous block with asolution of nonaethylene glycol in benzene for from one to two hours,removing excess impregnant from the block by draining and by drying at atemperature between 70 and C., and applying to the sides of the driedblock a relatively thin coating of from 5 to 10 mils thickness ofmaterial non-paste forming with the impregnant.

32. The method of making an electrical contact element including forminga porous block of finely divided metallic and graphitic electricallyconductive material, degassing the porous block by immersing in a 20% to40% solution of nonaethylene glycol in water and subjecting the blockfor one to two hours to a relatively low pressure such that the water ofthe solution boils, impregnating at least a part of the degassed porousblock at substantially atmospheric pressure with a 20% to 40% solutionof nonaethylene glycol in water for from one to two hours, removingexcess impregnant from the block by draining and by drying at atemperature between 70 and 120 0., and applying to the sides of thedried block a relatively thin coating of from 5 to 10 mils thickness ofmaterial non-paste forming with the impregnant.

ROBERT H. SAVAGE.

